exec

, eval

, source

形式

sh

exec [argument]...

eval [argument]...

csh

execcommand

evalargument...

source [-h] name

ksh88

*exec [argument]...

*eval [argument]...

ksh

+exec [-c] [-aname] [command [argument ... ]]

+eval [argument]...

機能説明

sh

The exec command specified by the arguments is executed in place of
this shell without creating a new process. Input/output arguments and appear and,
if no other arguments are specified, cause the shell input/output to be
modified.

The arguments to the eval built-in are read as input to the
shell and the resulting command(s) executed.

csh

exec executes command in place of the current shell, which terminates.

eval reads its arguments as input to the shell and executes the
resulting command(s). This is usually used to execute commands generated as the
result of command or variable substitution.

source reads commands from name. source commands can be nested, but if
they are nested too deeply the shell can run out of file
descriptors. An error in a sourced file at any level terminates all
nested source commands.

-h

Place commands from the file name on the history list without executing them.

ksh88

With the exec built-in, if arg is specified, the command specified by
the arguments is executed in place of this shell without creating a
new process. Input/output arguments can appear and affect the current process. If
no arguments are specified the effect of this command is to modify file
descriptors as prescribed by the input/output redirection list. In this case, any
file descriptor numbers greater than 2 that are opened with this mechanism
are closed when invoking another program.

The arguments to eval are read as input to the shell and
the resulting command(s) executed.

On this man page, ksh88(1) commands that are preceded by one or
two * (asterisks) are treated specially in the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.

I/O redirections are processed after variable assignments.

Errors cause a script that contains them to abort.

Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.

ksh

exec is a special built-in command that can be used to manipulate
file descriptors or to replace the current shell with a new command.

If command is specified, then the current shell process is replaced by
command rather than running command and waiting for it to complete. There
is no need to use exec to enhance performance since the shell implicitly
uses the exec mechanism internally whenever possible.

If no operands are specified, exec can be used to open or
close files, or to manipulate file descriptors from 0 to 9 in
the current shell environment using the standard redirection mechanism available with all
commands. The close-on-exec flags is set on file descriptor numbers greater than 2
that are opened this way so that they are closed when another
program is invoked.

Because exec is a special command, any failure causes the script that
invokes it to exit. This can be prevented by invoking exec from
the command utility.

exec cannot be invoked from a restricted shell to create files or
to open a file for writing or appending.

eval is a shell special built-in command that constructs a command by
concatenating the arguments together, separating each with a space. The resulting string
is taken as input to the shell and evaluated in the current
environment. command words are expanded twice, once to construct argument, and again when
the shell executes the constructed command. It is not an error if
argument is not specified.

On this manual page, ksh commands that are preceded by one or
two + symbols are special built-in commands and are treated specially in
the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.

I/O redirections are processed after variable assignments.

Errors cause a script that contains them to abort.

They are not valid function names.

Words following a command preceded by ++ that are in the format of a variable assignment are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and field splitting and file name generation are not performed.

オプション

ksh

The following options are supported by ksh exec:

-aname

argv[0] is set to name for command.

-c

Clear all environment variables before executions except variable assignments that are part of the current exec command.

終了ステータス

ksh88

The following exit values are returned by exec:

0

Successful completion.

1-125

A redirection error occurred.

127

command was not found.

126

command was found, but it is not an executable utility.

ksh

The following exit values are returned by exec. If command is specified,
exec does not return.

0

Successful completion. All I/O redirections were successful.

>0

An error occurred.

The following exit values are returned by eval:

If argument is not specified, the exit status is 0. Otherwise, it
is the exit status of the command defined by the argument operands.